AIM STEP 10
Student Memory Support
Peripheral Neuropathies and Neuromuscular Junction Disorders
4th Year MBBS • Neuroscience • High-yield memory reinforcement and last-minute revision
Structured according to the supplied Step 10 Student Memory Support requirements. :contentReference[oaicite:0]{index=0}
1. High-Yield Flashcards
Tap each question to reveal the answer.
What is the basic difference between neurapraxia and axonotmesis?
Neurapraxia causes conduction block with an intact axon; axonotmesis disrupts the axon and causes distal Wallerian degeneration.
What happens distal to a severely interrupted peripheral axon?
The distal axonal segment undergoes Wallerian degeneration.
What functional effect does segmental demyelination produce?
It slows nerve conduction and may cause conduction block.
Which peripheral neuropathy pattern affects several individual nerves asymmetrically?
Multiple mononeuropathies.
Why does a length-dependent neuropathy usually begin in the feet?
The longest axons have the greatest transport and maintenance demands and are affected first.
What is the classic motor pattern of Guillain–Barré syndrome?
Rapidly progressive, relatively symmetrical weakness with reduced or absent reflexes, commonly beginning in the legs.
What CSF pattern classically supports Guillain–Barré syndrome?
Raised CSF protein with relatively few cells: albuminocytologic dissociation.
Which two established immune therapies are used in Guillain–Barré syndrome?
Intravenous immunoglobulin and plasma exchange.
What pathological change may result from repeated demyelination and remyelination?
Onion-bulb formation around peripheral nerve fibers.
Which clinical pattern strongly suggests Charcot–Marie–Tooth disease?
Slowly progressive distal weakness with foot drop, steppage gait, pes cavus and reduced ankle reflexes.
Which nerve is compressed in carpal tunnel syndrome?
The median nerve beneath the flexor retinaculum.
Why may sensation over the thenar eminence be preserved in carpal tunnel syndrome?
The palmar cutaneous branch leaves the median nerve before it enters the carpal tunnel.
What is the core pathophysiological defect in autoimmune myasthenia gravis?
Autoimmune postsynaptic dysfunction reduces effective acetylcholine receptor activity and the safety margin of neuromuscular transmission.
How does pyridostigmine improve weakness in myasthenia gravis?
It inhibits acetylcholinesterase, increasing acetylcholine availability at the neuromuscular junction.
2. Mnemonics
Mnemonic Title: Peripheral Neuropathy Distribution
MAP
Meaning: Mononeuropathy → Asymmetric multiple mononeuropathies → Polyneuropathy.
Mnemonic Title: Myasthenia Gravis Core Pattern
FAR
Meaning: Fatigable weakness → Acetylcholine-receptor dysfunction → improvement with Rest.
3. Memory Tables
Peripheral Nerve Injury Types
| Feature | Neurapraxia | Axonotmesis | Neurotmesis |
|---|---|---|---|
| Axon | Intact | Disrupted | Completely disrupted |
| Wallerian degeneration | Absent | Present distally | Present distally |
| Recovery | Generally good | Possible if pathways preserved | Poor without repair |
GBS vs Myasthenia Gravis
| Feature | Guillain–Barré Syndrome | Myasthenia Gravis |
|---|---|---|
| Main site | Peripheral nerves / roots | Postsynaptic neuromuscular junction |
| Weakness pattern | Acute, often ascending | Fluctuating and fatigable |
| Reflexes | Reduced or absent | Generally preserved |
| Sensation | Paresthesia may occur | Normal |
| Key therapy | IVIG or plasma exchange | Pyridostigmine ± immunosuppression |
4. Rapid Revision Points — Last-Minute Revision
Must Remember:
- Neurapraxia is conduction block without axonal discontinuity.
- Axonotmesis causes Wallerian degeneration but may recover if supporting pathways remain intact.
- Neurotmesis has poor spontaneous recovery and may require surgical repair.
- Stocking–glove sensory loss suggests a length-dependent polyneuropathy.
- GBS produces acute symmetrical weakness with reduced or absent reflexes.
- Respiratory, bulbar and autonomic involvement are major danger features in GBS.
- Repeated demyelination and remyelination may produce onion-bulb formations.
- CMT commonly causes distal wasting, foot drop, steppage gait and pes cavus.
- Carpal tunnel syndrome causes median-distribution paresthesia and may progress to thenar weakness.
- Myasthenia gravis causes fatigable weakness with normal sensation and generally preserved reflexes.
KMU Exam Trap: GBS is a peripheral neuropathy with areflexia; myasthenia gravis is a neuromuscular junction disorder with generally preserved reflexes.
5. Clinical Memory Hooks
Post-infectious rapidly ascending weakness with areflexia
→
Guillain–Barré syndrome.
→
Guillain–Barré syndrome.
Young patient with foot drop, steppage gait and pes cavus
→
hereditary peripheral neuropathy such as Charcot–Marie–Tooth disease.
→
hereditary peripheral neuropathy such as Charcot–Marie–Tooth disease.
Nocturnal thumb, index and middle-finger paresthesia
→
median nerve compression in the carpal tunnel.
→
median nerve compression in the carpal tunnel.
Ptosis and diplopia worsening with repeated activity
→
myasthenia gravis due to impaired postsynaptic neuromuscular transmission.
→
myasthenia gravis due to impaired postsynaptic neuromuscular transmission.
6. Starred High-Yield Exam Points
- ⭐ Wallerian degeneration occurs distal to a significantly interrupted peripheral axon.
- ⭐ Albuminocytologic dissociation supports Guillain–Barré syndrome.
- ⭐ IVIG and plasma exchange are established disease-modifying treatments for GBS.
- ⭐ Onion-bulb formation indicates repeated peripheral demyelination and remyelination.
- ⭐ Thenar wasting in carpal tunnel syndrome suggests advanced median nerve dysfunction.
- ⭐ Myasthenic crisis causes severe bulbar or respiratory weakness and requires urgent airway and ventilatory support.